CENTRIOLES AND BASAL BODIES 51 



that they can hardly grow out directly from the centriole wall 

 fibrils. Amano (1957) has suggested the presence of two types of 

 spindle fibre; nine gross spindle fibres seen under the phase 

 contrast microscope, and fine '* chromosome fibres " correspond- 

 ing in number to the chromosomes present in that type of cell. 

 According to Amano, the former type of fibril is tubular, but the 

 latter type is not. In the meiotic spindle of the crayfish Cambarus, 

 Ruthmann (1959) found that at the first division two centrioles 

 were present at each spindle pole, and that the axes of the two 

 centrioles and the spindle were all three mutually at right angles ; 

 only one centriole was present at each spindle pole at the second 

 division. It is by no means certain that the spindle fibres are 

 formed directly by the centriole, in fact Ruthmann found that the 

 endoplasmic reticulum (as described by Palade and Porter) contri- 

 buted a great deal to the spindle structure, so that the function of 

 the centriole may be to organize the orientation of cytoplasmic 

 components. 



A rather similar appearance of the organization of cytoplasmic 

 vesicles was found in the developing ciliary bud of the chick 

 neural epithelium by Sotelo and Trujillo-Cenoz (1958) (Fig. 12). 

 Here each epithelial cell develops one cilium shortly after its 

 formation by the division of an undifferentiated cell. At the cell 

 division, two centrioles orientated at right angles are associated 

 with the nucleus of each daughter cell. After the division both 

 centrioles migrate to the free surface of the cell, where one makes 

 contact with the cell surface, while the other takes up a position on 

 the same longitudinal axis as, and towards the centre of the cell from, 

 the first centriole. The second centriole often remains transverse 

 in sperm. Contact between the centriole and the cell membrane 

 initiates the formation of the ciliary bud, and, for the first time in 

 this study, a cross -membrane is seen closing the distal end of the 

 outer centriole. There is uncertainty about the permanence of a 

 membrane or granule in this position, for Rouiller and Faure- 

 Fremiet (1958) found that a granule was formed during cilium 

 growth, while Burgos and Fawcett (1956) figure the proximal 

 (transverse) centriole of the cat spermatid which carries a granule 

 although it is not directly connected to the flagellar axis of the tail. 



Within the fairly broad ciliary bud, which is formed by a 

 protrusion of the cell membrane, is a cytoplasmic matrix with 



